This invention relates generally to computer systems, and more particularly to graphical user interfaces for computer systems.
Graphical user interfaces or GUI are becoming increasingly popular with computer users. It is generally accepted that computers having graphical user interfaces are easier to use, and that it is quicker to learn an application program in a GUI environment than in a non-GUI environment.
A relatively new type of computer which is well suited for graphical user environments is the pen-based computer system. A pen-based computer system is typically a small, hand-held computer where the primary method for inputting data includes a "pen" or stylus. A pen-based computer system is often housed in a relatively flat enclosure, and has a dual-function display assembly which serves as both an input device and an output device. When operating as an input device, the display assembly senses the position of the tip of a stylus on the viewing screen and provides this positional information to the computer's central processing unit (CPU). Some display assemblies can also sense the pressure of the stylus on the screen to provide further information to the CPU. When operating as an output device, the display assembly presents computer-generated images on the screen.
The dual-function display assemblies of pen-based computer systems permit users to operate the computer as a computerized notepad. For example, graphical images can be input into the pen-based computer by merely moving the stylus across the surface of the screen. As the CPU senses the position and movement of the stylus, it generates a corresponding image on the screen to create the illusion that the stylus is drawing the image directly upon the screen, i.e. that the stylus is "inking" an image on the screen. With suitable recognition software, text and numeric information can also be entered into the pen-based computer system in a similar fashion. Besides serving as a notepad, pen-based computers can provide a number of useful functions, such as serving as an address book, an appointment calendar, a to-do list, etc.
It is often desirable to be able to move or copy objects (i.e. associated images) on a computer screen. These objects can be moved within a single application program (e.g. a notepad application program) or between two different application programs (e.g. between a notepad application program and a calendar application program). The term "object" as used herein means any selected text, graphic, or other image on the computer screen which is to be moved or copied as a unit.
In the prior art, a move or copy is often accomplished with a conceptual device known as a "clipboard." For example, to copy an object, the object is first selected on a computer screen by means of some type of pointing device such as a mouse, trackball, etc., and the selected object is then copied into an area of memory used by the clipboard. The pointing device is then used to indicate where the content of the clipboard is to be inserted, and then the content of the clipboard is "pasted" into the application program at the indicated location. A move is accomplished in substantially the same manner as a copy, except the selected object removed from the original place on the screen. These processes are sometimes referred to as "copy-and-paste" and "cut-and-paste", respectively.
A problem with prior art clipboards is that they are invisible to the user. Users can therefore forget that they have something stored in the clipboard, or they may forget what is in the clipboard. This can result in a variety of errors. For example, if a user is interrupted during a move process and forgets to paste the object back into an application program. The contents of the clipboard may be permanently lost. Also, if the user forgets what the content of the clipboard is, they may inadvertently paste incorrect objects into an application program. Furthermore, since the clipboard is invisible, it is difficult to provide multiple clipboards storing a variety of objects.